The molecular and physiological mechanisms involved in myocardial cytosolic and mitochondrial creatine kinase (CK) release and turnover will be characterized including the mechanism for plasma CK isoforms and whether their release reflects irreversible injury. The data will be used ot improve estimation of infarct size by addresssing existing limitations, namely, inability to obtain individual CK disappearance rates (k/d), inability to account for the fate of CK depleted from myocaridium and the inaccuracy of estimates during reperfusion. Myocardial infarction will be induced in conscious animals, CK will be sampled simultaneously from blood and an indwelling catheter in the cardiac lymphatics. Infarct size will be estimated from plasma CK with and without reperfusion and compared to histological estimates and CK depletion. The true elimination rate for CK (k/d) will be determined from steady state kinetics during an infusion of the different CK isoforms. The rate of infusion of CK to maintain a constant plasma level reflects the rate of removal from the circulation. The CK k/d estimated from bolus injections by monexponential and biexponential fits and the individual k/d from the downslope of the plasma CK curve estimated after quantitative exclusion of newly released tissue CK isoform will be compared to the k/d determined from steady state kinetics in the same animal. Liver perfusion experiments will be performed to assess the mechanism of removal CK. Using radioimmunoassays for both nitochondrial and cytosolic CK, release into plasma after coronary occlusion will be compared to light and electron microscopic analysis of myocardium as well as deposition of I125labelled F(ab')2 fragments to CK. In vivo conversion of CK, to the isoforms will be characterized and the isoforms validated for detecting reperfusion. Methods to rapidly quantify CK isoforms will be validated as will isoform release as a marker of reperfusion against coronary angiography. Accurate estmates of infarct size during reperfusion would reduce the number of patients required to assess thrombolytic therapy. Early implementation of IV thromboyltic therapy emphasizes the need for early diagnosis as well as noninvasive means to detect reperfusion. Molecular mechanisms underlying removal of CK have implications for other enzymes and proteins including therapy for enzyme deficiencies. Assessment of myocardial F(ab')2 uptake is important background for in vivo assessment of sarcolemma and mitochondrial membrane integrity as well as for future means of targeting specific therapies.